1. Technical Field
This invention relates to the field of polymers and more specifically to the field of articles prepared from polypropylene homopolymers and copolymers.
2. Background of the Art
Homopolymers and copolymers of polypropylene are typically polymerized in continuous polymerization reactors, such as, for example, loop reactors. To produce these polymers one or more monomer streams are generally introduced into the selected reactor and then circulated with an appropriate catalyst. Frequently, conventional Ziegler-Natta catalysts are employed. The resulting polymers may be subjected to appropriate purification and post-processing steps and then made into end products using conventional techniques such as injection molding and extrusion. These end products may be, for example, films, molded articles, and fibers, as well as the woven and non-woven products that may be prepared from the fibers.
Unfortunately, Ziegler-Natta catalyzed polypropylene products often suffer from certain undesirable physical and mechanical properties problems. For example, films may exhibit undesirably poor clarity, which reduces their commercial potential. Molded parts may exhibit reduced smoothness, strength and toughness. Fibers, too, may show less than desirable levels of strength and toughness, which may result in problems during weaving or other steps necessary to prepare end products therefrom. Because of these problems, a need exists for articles of manufacture, prepared from polypropylene materials, in which these problems are reduced or eliminated.